Laser radiation, e.g., 10.6 .mu.m infrared (IR) radiation from CO.sub.2 lasers, has found numerous applications in industry as well as in medicine. Among uses in industry are welding, soldering, cutting, laser annealing, scribing and drilling of substrates, and trimming of resistors. In medicine, typical applications of IR laser radiation are in ophthalmic retinal photocoagulation, and in dermatological, laryngological, and gynecological surgery.
The provision of a flexible path for IR radiation between the source and a variably positioned target has proved a difficult problem, and many solutions therefor have been proposed. Among such solutions are IR transmitting fibers, flexible metal waveguides, and conventional articulated arms.
IR-transmitting fiberguides are known in the art. For instance, D. A. Pinnow et al, Applied Physics Letters, Vol. 33(1), pp. 28-29, 1978 disclose polycrystalline thallium bromo-iodide and thallium bromide fibers which, according to these authors, have transmission loss and power handling capability satisfactory for image relay applications and surgical studies. However, the disclosed fibers are mechanically fragile, and for this and other reasons require a protective cladding. The above authors teach that the polycrystalline cores are inserted into a loose-fitting polymer cladding, which serves both as a means for optical confinement of the guided modes and as a means for mechanical protection of the fiber. However, it has been found that fibers of such construction lack PG,4 mechanical strength. T. Hidaka et al, Journal of Applied Physics, Vol. 52(7), pp. 4467-4471, 1981. A medical laser instrument incorporating IR-transmitting fiber is disclosed in U.S. Pat. No. 4,170,997, issued Oct. 16, 1979 to D. A. Pinnow and A. L. Gentile.
In addition to the already mentioned fragility of the above described fiber, such fibers have further disadvantageous properties. In particular, single mode radiation from a laser coupled into such fiber typically rapidly degrades into multiple mode radiation, whose output pattern changes in form as the radiation path is changed. This degradation considerably reduces the maximum output energy density that can be obtained, and thus diminishes the utility of an IR laser device for many of the above-cited applications, since these typically require achievement of high energy density over a very small target area.
The use of a flexible, hollow metal waveguide for providing a radiation path between an IR radiation source and a variably positioned target was proposed by E. Garmire et al, Applied Physics Letters, Vol. 34(1), pp. 35-37, 1979. Although such guides can be constructed with sufficient mechanical stability, they typically also result in degradation of single mode radiation into multiple mode form, and thus suffer also from the above described shortcoming.
The use of articulated arms of conventional design as means for providing a flexible radiation path for IR laser radiation has been frequently disclosed. See, for instance, U.S. Pat. No. 3,658,406, issued Apr. 25, 1972 to N. Karube and Y. Morita; U.S. Pat. No. 3,913,582, issued Oct. 21, 1975, to U. Sharon; and U.S. Pat. No. 4,122,853, issued Oct. 31, 1978 to M. R. Smith. Articulated arms of conventional design consist of movably connected straight sections of, e.g., metal tubing, through whose bore a beam of unguided radiation can travel axially. The input beam diameter is typically considerably less than the bore diameter, but the beam diameter increases with increasing propagation distance due to diffraction spreading. Means for changing the propagation direction of the beam are placed at the junctions between adjacent straight sections of tubing, thus allowing maintenance of the axial propagation of the beam through a multiplesegment arm. Typical beam direction altering means are mirrors or prisms.
Single mode IR radiation launched into an articulated arm of conventional design typically remains single mode. However, unless the input beam is launched precisely on axis, and unless the arm is constructed to very close tolerances, such that the beam remains on axis regardless of configuration and orientation of the arm, the output beam will deviate from the axial direction of the output segment, and wander in a complicated manner as the arm is manipulated, i.e., such arms typically have low pointing accuracy. By "pointing accuracy," we mean herein the closeness of the direction of the output beam to the axis of the output segment of the arm, and "low" pointing accuracy refers to substantial beam deviation from the tube axis, typically in excess of about 1 degree. Since the applications of high intensity IR laser radiation typically require that the beam energy be directed to a predetermined and generally very small target region, typically much less than 1 mm.sup.2, it is clear that low pointing accuracy constitutes a considerable drawback in a device for conveying the radiation to the target. In addition to having low pointing accuracy, articulated arms of conventional design typically also are large and cumbersome, requiring counterweighting to permit precise control of the arm without application of substantial force, as required, for instance, for application in eye surgery.
The prior art means for providing a flexible radiation path between an IR laser source and a moving or movable target thus have shortcomings that make it difficult to realize the full potential of IR radiation in industrial and medical applications, and a radiation delivery system not subject to these shortcomings would inter alia be of considerable commercial interest.